This invention relates to a control signal generator for use in combination with a television signal codec, namely, a television signal encoder and/or a television signal decoder.
A television signal encoder is disclosed in U.S. Pat. No. 4,006,297 issued to Toshio Koga and assigned to the present assignee. One of control signals used in such a television signal encoder, is for suspending the encoding operation during each horizontal blanking period. More particularly, it is usual to raise the efficiency of encoding by making a television signal encoder encode only one horizontal blanking period in a first horizontal scanning line as a representative of like horizontal blanking periods which appear at regular intervals in the respective horizontal scanning lines. For a quantizer used in an encoder for a color television signal comprising video signals and color bursts, a similar control signal is used to carry out switching between quantization steps for each video signal and for each color burst because the video signal has a signal level which is very rapidly variable as compared with the color burst.
As will later be described with reference to one of several figures of the accompanying drawing, such a control signal may go out of phase synchronism with the horizontal synchronizing signals. In this event, a television signal decoder can not correctly reproduce an original television signal which is encoded by the encoder into an encoded television signal for conveyance to the decoder. For example, deterioration takes place in the encoding or the quantization characteristics when the control signal is out of the phase synchronism. The circumstances are not different even when the control signal is phase synchronized with the vertical synchronizing signals. Incidentally, a sequence of horizontal or vertical synchronizing signals will collectively be called a horizontal or a vertical synchronizing signal as the case may be.